Lymphocytes are one of several populations of white blood cells; they specifically recognize and respond to foreign antigen. The three major classes of lymphocytes are B lymphocytes (B cells), T lymphocytes (T cells) and natural killer (NK) cells. B lymphocytes are the cells responsible for antibody production and provide humoral immunity. B cells mature within the bone marrow and leave the marrow expressing an antigen-binding antibody on their cell surface. When a naive B cell first encounters the antigen for which its membrane-bound antibody is specific, the cell begins to divide rapidly and its progeny differentiate into memory B cells and effector cells called plasma cells. Memory B cells have a longer life span and continue to express membrane-bound antibody with the same specificity as the original parent cell. Plasma cells do not produce membrane-bound antibody but instead produce secreted form of the antibody. Secreted antibodies are the major effector molecules of humoral immunity.
A group of tumor necrosis factor (TNF) receptors found on the surface of B cells under various conditions are among the cellular regulators of B cell function in the immune system. In particular, three TNF receptors: transmembrane activator and CAML interactor (TACI), B cell activator belonging to the TNF family receptor (BAFF—R), and B cell maturation protein (BCMA) are known to bind one or both TNF ligands—B Lymphocyte stimulator (BLyS also known as BAFF, TALL-1, ztnf4 and THANK) and a proliferation-inducing ligand (APRIL). Specifically, TACI and BCMA are known to bind both BLyS and APRIL and BAFF—R binds only BLyS.
A number of BLyS antagonists have been developed in order to block the various functions of BLyS, which include but should not be limited to B cell co-stimulation, plasmablast and plasma cell survival, Ig class switching, enhanced B-cell antigen presenting cell function, survival of malignant B cells, development of B-1 cell function, B cell development beyond the T-1 stage, and complete germinal centre formation Some of these molecules can also bind to and block the effect of APRIL on B cells and other components of the immune system (Dillon et al. (2006) Nat. Rev. Drug Dis. 5, 235-246). Molecules that have been developed to affect B cell function by interfering with BLyS and/or APRIL binding include BLyS antibodies such as Lymphostat-B (Belimumab) (Baker et al, (2003) Arthritis Rheum, 48, 3253-3265 and WO 02/02641); receptor-extracellular domain/Fc domain fusions proteins such as TACI-Ig, including one particular embodiment, atacicept (U.S. Patent Application No. 20060034852), BAFF—R-Fc (WO 05/0000351), and BCMA-Ig or other fusion proteins utilizing receptor extracellular domains. A further class of BLyS antagonists include other molecules relying on BLyS binding ability to block binding to its receptors such as AMG 623, receptor antibodies, and other molecules disclosed in WO 03/035846 and WO 02/16312.
The CD20 antigen (also called human B-lymphocyte-restricted differentiation antigen, Bp35) is a hydrophobic transmembrane protein with a molecular weight of approximately 35 kD located on pre-B and mature B lymphocytes (Valentine et al. J. Biol. Chent. 264 (19): 11282-11287 (1989); and Einfeld et al. EMBO J. 7 (3): 711-717 (1988)). The antigen is also expressed on greater than 90% of B cell non-Hodgkin's lymphomas (NHL) (Anderson et al. Blood 63 (6): 1424-1433 (1984)), but is not found on hematopoietic stem cells, pro-B cells, normal plasma cells or other normal tissues (Tedder et al. J. Immunol. 135 (2): 973-979 (1985)). CD20 regulates an early step (s) in the activation process for cell cycle initiation and differentiation (Tedder et al., supra) and possibly functions as a calcium ion channel (Tedder et al. J. Cell. Biochem. 14D: 195 (1990)).
Given the expression of CD20 on B cells, this antigen can serve as a candidate for “targeting” of those cells to treat autoimmune diseases. In essence, such targeting can be generalized as follows: antibodies specific to the CD20 surface antigen of B cells are administered to a patient. These anti-CD20 antibodies specifically bind to the CD20 antigen of (ostensibly) both B cells producing normal antibodies and detrimental autoantibodies; the antibody bound to the CD20 surface antigen may lead to the destruction and depletion of these B cells. Irrespective of the approach, a primary goal is to destroy the cells producing the autoantibodies; the specific approach can be determined by the particular anti-CD20 antibody which is utilized and, thus, the available approaches to targeting the CD20 antigen can vary considerably.
The rituximab (RITUXAN®) antibody is a genetically engineered chimeric murine/human monoclonal antibody directed against the CD20 antigen. Rituximab is the antibody called “C2B8” in U.S. Pat. No. 5,736,137 issued Apr. 7, 1998 (Anderson et al.).
RITUXAN® (rituximab) has been approved for the treatment of patients with relapsed or refractory low-grade or follicular, CD20 positive, B cell non-Hodgkin's lymphoma. In vitro mechanism of action studies have demonstrated that RITUXAN® (rituximab) binds human complement and lyses lymphoid B cell lines through complement-dependent cytotoxicity (CDC) (Reff et al. Blood 83 (2): 435-445 (1994)). Additionally, it has significant activity in assays for antibody-dependent cellular cytotoxicity (ADCC). More recently, RITUXAN® (rituximab) has been shown to have anti-proliferative effects in tritiated thymidine incorporation assays and to induce apoptosis directly, while other anti-CD19 and CD20 antibodies do not (Maloney et al. Blood 88 (10): 637a (1996)). Synergy between RITUXAN (rituximab) nd chemotherapies and toxins has also been observed experimentally.
In particular, RITUXAN® (rituximab) sensitizes drug-resistant human B cell lymphoma cell lines to the cytotoxic effects of doxorubicin, CDDP, VP-16, diphtheria toxin and ricin (Demidem et al., Cancer Chemotherapy & Radiopharmaceuticals 12 (3): 177-186 (1997)). In vivo preclinical studies have shown that RITUXAN® (rituximab) depletes B cells from the peripheral blood, lymph nodes, and bone marrow of cynomolgus monkeys, presumably through complement and cell-mediated processes (Reff et al. Blood 83 (2): 435-445 (1994)).
Patents and patent publications concerning CD20 antibodies include U.S. Pat. Nos. 5,776,456; 5,736,137; 6,399,061; and 5,843,439, as well as US patent appln nos. US 2002/0197255A1, US 2003/0021781A1, US 2003/0082172 A1, US 2003/0095963 A1, US 2003/0147885 A1 (Anderson et al.); U.S. Pat. No. 6,455,043B1 and WO00/09160 (Grillo-Lopez, A.); WO00/27428 (Grillo-Lopez and White); WO0/27433 (Grillo-Lopez and Leonard); WO0/44788 (Braslawsky et al.); WO01/10462 (Rastetter, W.); WO01/10461 (Rastetter and White); WO01/10460 (White and Grillo-Lopez); US appln no. US2002/0006404 and WO02/04021 (Hanna and Hariharan); US appln no. US2002/0012665 A1 and WO01/74388 (Hanna, N.); US appln no. US 2002/0058029 A1 (Hanna, N.); US appln no. US 2003/0103971 A1 (Hariharan and Hanna); US appln no. US2002/0009444A1, and WO01/80884 (Grillo-Lopez, A.); WO01/97858 (White, C.); US appln no. US2002/0128488A1 and WO02/34790 (Reff, M.); WO02/060955 (Braslawsky et al.); WO2/096948 (Braslawsky et al.); WO02/079255 (Reff and Davies); U.S. Pat. No. 6,171,586B1, and WO98/56418 (Lam et al); WO98/58964 (Raju, S.); WO99/22764 (Raju, S.); WO99/51642, U.S. Pat. Nos. 6,194,551B1, 6,242,195B1, 6,528,624B1 and 6,538,124 (Idusogie et al.); WO/42072 (Presta, L.); WO00/67796 (Curd et al.); WO01/03734 (Grillo-Lopez et al.); US appln no. US 2002/0004587A1 and WO01/77342 (Miller and Presta); US appln no. US2002/0197256 (Grewal, I); US Appln no. US 2003/0157108 A1 (Presta, L.); U.S. Pat. Nos. 6,090,365B1, 6,287,537B1, 6,015,542, 5,843,398, and 5,595,721, (Kaminski et al.); U.S. Pat. Nos. 5,500,362; 5,677,180; 5,721,108; and 6,120,767 (Robinson et al.); U.S. Pat. No. 6,410,391B1 (Raubitschek et al.); U.S. Pat. No. 6,224,866B1 and WO00/20864 (Barbera-Guillem, E.); WO01/13945 (Barbera-Guillem, E.); WO00/67795 (Goldenberg); US Appl No. US 2003/01339301 A1 and WO00/74718 (Goldenberg and Hansen); WO/76542 (Golay et al.); WO01/72333 (Wolin and Rosenblatt); U.S. Pat. No. 6,368,596B1 (Ghetie et al.); US Appln no. US2002/0041847 A1, (Goldenberg, D.); US Appln no. US2003/0026801A1 (Weiner and Hartmann); WO02/102312 (Engleman, E.); US Patent Application No. 2003/0068664 (Albitar et al.); WO03/002607 (Leung, S.); WO049694 (Wolin et al.); WO03/061694 (Sing and Siegall), each of which is expressly incorporated herein by reference. See, also, U.S. Pat. No. 5,849,898 and EP appln no. 330,191 (Seed et al.); U.S. Pat. No. 4,861,579 and EP332, 865A2 (Meyer and Weiss); U.S. Pat. No. 4,861,579 (Meyer et al.) and WO95/03770 (Bhat et al.).
Publications concerning therapy with Rituximab include: Perotta and Abuel “Response of chronic relapsing ITP of 10 years duration to Rituximab” Abstract # 3360 Blood 10 (1) (part 1-2): p. 88B (1998); Stashi et al. “Rituximab chimeric anti-CD20 monoclonal antibody treatment for adults with chronic idopathic thrombocytopenic purpura” Blood 98 (4): 952-957 (2001); Matthews, R. “Medical Heretics” New Scientist (7 Apr. 2001); Leandro et al. “Clinical outcome in 22 patients with rheumatoid arthritis treated with B lymphocyte depletion” Ann Rheum Dis 61: 833-888 (2002); Leandro et al. “Lymphocyte depletion in rheumatoid arthritis: early evidence for safety, efficacy and dose response. Arthritis and Rheumatism 44 (9): S370 (2001); Leandro et al. “An open study of B lymphocyte depletion in systemic lupus erythematosus”, Arthritis & Rheumatism 46 (1): 2673-2677 (2002); Edwards and Cambridge “Sustained improvement in rheumatoid arthritis following a protocol designed to deplete B lymphocytes” Rhematology 40: 205-211 (2001); Edwards et al. “B-lymphocyte depletion therapy in rheumatoid arthritis and other autoimmune disorders” Biochem. Soc. Trans. 30 (4): 824-828 (2002); Edwards et al. “Efficacy and safety of Rituximab, a B-cell targeted chimeric monoclonal antibody: A randomized, placebo controlled trial in patients with rheumatoid arthritis. Arthritis and Rheumatism 46 (9): S197 (2002); Levine and Pestronk “IgM antibody-related polyneuropathies: B-cell depletion chemotherapy using Rituximab” Neurology 52: 1701-1704 (1999); DeVita et al. “Efficacy of selective B cell blockade in the treatment of rheumatoid arthritis” Arthritis & Rheum 46: 2029-2033 (2002); Hidashida et al. “Treatment of DMARD-Refractory rheumatoid arthritis with rituximab.” Presented at the Anfzual Sciehtific Meeting of the American College of Rheumatology; October 24-29; New Orleans, La. 2002; Tuscano, J. “Successful treatment of Infliximab-refractory rheumatoid arthritis with rituximab” Presented at the Annual Scientific Meeting of the American College of Rheumatology; October 24-29; New Orleans, La. 2002.